Web site musicForProgramming(); distributes a series of roughly hour-long ambient music mixes intended to "aid concentration and increase productivity" while you work.

Despite the name, the site's mixes are, of course, suitable for anyone. Their aesthetic manifesto:

Through years of trial and error - skipping around internet radio stations, playing our entire music collections on shuffle, or just hammering single albums on repeat, we have found that the most effective music to aid prolonged periods of intense concentration tends to have a mixture of the following qualities:

Music possessing these qualities can often provide just the right amount of interest to occupy the parts of your brain that would otherwise be left free to wander and lead to distraction during your work.

True or not, the four current mixes on the site feature music from some musicians I'd happily listen to during a heads-down work session, including Philip Glass (he of many great minimalist film scores) and Cliff Martinez (who did the score for the movie Drive, which has also incidentally been featured in Work Sounds). If you're looking for some good music to work to, musicForProgramming() has some nice offerings.